In the automobile industory or the machinery industory, there has been increased demand for detectors capable of precisely detecting a physical quantity such as force, acceleration or magnetism. Particularly, it is required to realize small detectors capable of detecting physical quantities having two dimensional or three dimensional components.
To meet such a demand, there has been proposed a force detector in which gauge resistors are formed on a semiconductor substrate such as silicon, etc. to transform a mechanical distortion produced in the substrate on the basis of a force applied from the external to an electric signal by making use of the piezo resistance effect. When a weight body is attached to the detecting unit of the force detector, an acceleration detector for detecting, as a force, an acceleration applied to the weight body can be realized. Further, when a magnetic body is attached to the detecting unit of the force detector, a magnetic detector for detecting, as a force, a magnetism exerted on the magnetic body can be realized. For example, in U.S. Pat. No. 4,905,523, U.S. Pat. No. 4,967,605, U.S. Pat. No. 4,969,366, detectors for force, acceleration or magnetism according to the invention by the inventor of this application are disclosed.
In place of the above described detectors utilizing the piezo resistance effect, detectors utilizing changes in distance between electrodes are proposed. For example, in the Japanese Patent Application No. 274299/90 specification, there is disclosed a detector of a simple structure including two substrates oppositely arranged and electrodes formed on respective substrates. In this detector, one substrate is allowed to be subjected to displacement on the basis of a physical action such as force, acceleration, or magnetism, etc. to be detected. An applied force changes the distance between electrodes formed on both the substrates. By this displacement the applied force is detected as a change of an electrostatic capacity between both the electrodes, Alternatively, there is also disclosed a method in which a piezo electric element is put between both electrodes to detect a change of the distance between the electrodes as a voltage produced from the piezo electric element. If an external force is directly exerted to one substrate, this detector functions as a force detector for detecting an external force exerted. Further, if a weight body is connected to one substrate so that the substrate is subjected to displacement on the basis of an acceleration exerted on the weight body, this detector functions as an acceleration detector for detecting an acceleration exerted. In addition, if a magnetic body is connected to one substrate so that the substrate is subjected to displacement on the basis of a magnetism exerted on the magnetic body, this detector functions as a magnetic detector for detecting a magnetism exerted.
Generally, in the case of providing apparatuses for detecting any physical quantity as commercial products, there takes place the necessity of carrying out an operation test as to whether or not this detector outputs a correct detection signal. As such an operation test, there is adopted a method of actually exerting a physical quantity to be detected on that detector to examine a detection signal at that time. For example, in the case of an acceleration detector, there is employed a method of actually applying, from a predetermined direction, an acceleration of a predetermined magnitude to the detector to judge whether or not a detection signal at that time is a correct one corresponding to the applied acceleration. However, in order to carry out such an operation test, a test equipment exclusively used therefor is required, and the test work is complicated or troublesome, requiring much time. Especially, the quantity of detectors which can be tested by an exclusive test equipment is limited, resulting in lowered productivity. Accordingly, such a conventional test method is not suitable as the method of testing the operation of detectors mass produced.
A first object of this invention is to provide a method capable of conducting a simple operation test of apparatuses for detecting a physical quantity utilizing changes in distance between electrodes, and a second object thereof is to provide a detector having a self diagnostic function by this simple operation test method.